USB: EHCI: consolidate code in ehci_urb_dequeue()

This patch (as1668) consolidates two nearly identical code paths in
ehci_urb_dequeue().  The test for !qh can be removed because it will
never succeed; the fact that usb_hcd_check_unlink_urb() returned 0
means that urb must be queued and therefore urb->hcpriv must point to
a QH.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>